1. Field of the Invention
The present invention relates to a magnetic memory.
2. Related Background Art
A MRAM (Magnetic Random Access Memory) has attracted attention as a non-volatile memory. The MRAM stores information by controlling a magnetization direction of a free layer (sensitive magnetic layer) with respect to a magnetization direction of a fixed layer, and reads the stored information by measuring the amount of electrons (electrical resistance) transmitting through the free layer. The amount of electrons transmitting through a memory element, i.e., the magnetic resistance, is changed by the difference between the magnetization directions of the free layer and the fixed layer, thus the value that is obtained when the magnetization directions of both layers are parallel and the magnetic resistance is low is set to, for example, “0,” and the value that is obtained when the magnetization directions of both layers are antiparallel and the magnetic resistance is high is set to, for example, “1.”
When writing information to each memory element, an electrical wire is disposed in the vicinity of the memory element, and the magnetization direction of the free layer is changed by means of a magnetic induction field generated by applying current to the electrical wire. Recently, there has been known a magnetic memory that writes information by injecting a spin to a free layer, while performing magnetic-field assistance (for example, see W. C. Jeong, J. H. Park, J. H. Oh, G. T. Jeong, H. S. Jeong, and Kinam Kim. “Highly scalable MRAM using field assisted current induced switching.” Symposium on VLSI Technology Digest of Technical Papers (2005): P. 184-185).
Incidentally, high integration of the MRAM by miniaturizing each memory element has been studied. According to the “scaling law” of a semiconductor technology, high integration and electrical power saving can be achieved by reducing a certain element three-dimensionally and, at the same time, changing the impurity concentration and power supply voltage at the same rate.
It is considered that the abovementioned technical common knowledge of the semiconductor technology applies to a magnetic memory to a certain extent. That is, it is self-evident that a large external magnetic field (write current) is required to change the magnetization direction of an extremely large magnetic substance, and that a relatively small external magnetic field is sufficient to change the magnetization direction of a small magnetic substance. In other words, the amount of write current required to invert the magnetization of a free layer decreases by reducing the dimension of the element.